Thin film transistor, fabricating method of thin film transistor and display device using the same

ABSTRACT

A thin film transistor comprises: a first transistor region and a second transistor region defined on a substrate; and a first transistor and a second transistor respectively disposed on the first and second transistor regions, the first transistor comprising: a first semiconductor layer having source, channel, and drain regions defined on the substrate; a first insulating film disposed on the first semiconductor layer; a first transparent electrode disposed on the first insulating film and formed corresponding to the channel region of the first semiconductor layer; and a second insulating film disposed on the first transparent electrode, and the second transistor comprising: a second semiconductor layer having source, channel, and drain regions defined on the substrate; the first insulating film disposed on the second semiconductor layer; a second transparent electrode disposed on the first insulating film and formed corresponding to the channel region of the second semiconductor layer; a second gate disposed on the second transparent electrode; and the second insulating film disposed on the second gate.

RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2008-124244 filed on Dec. 8, 2008, which is hereby incorporated byreference in its entirety.

BACKGROUND

1. Field

This document relates to a thin film transistor, a fabricating method ofa thin film transistor, and a display device using the same.

2. Related Art

With the development of the information technology, the market ofdisplay devices, that is, connection media between users and informationhas been expanded. In line with this trend, the use of a flat paneldisplay (FPD), such as a liquid crystal display (LCD), an organic lightemitting diode (OLED), and a plasma display panel (PDP), has increasing.Of these, a liquid crystal display, which can implement highresolutions, can be miniaturized and made and can have a large screensize, has been widely used.

Some of the above-mentioned display devices display an image by beingdriven by thin film transistors formed on a substrate and data stored incapacitors. The thin film transistor may include a gate, a semiconductorlayer, a source, and a drain which are formed on a substrate.

Representative display devices driven by thin film transistors includean organic light emitting display and a liquid crystal display. Theorganic light emitting display is classified as a self-luminous displaydevice, and the liquid crystal display is classified as alight-receiving type display device.

Each of these display devices may have a normal transistor that operatesby a voltage supplied to the gate during a thin film transistorformation process and a phototransistor that operates by a channelformed by an external light. Herein, the phototransistor, which is asensor, is configured circuitally so as to adjust the luminance of apanel by external light.

Conventionally, in a thin film transistor process, an additionalprocess, such as the formation of a doping mask, is performed to dopesource and drain regions of a transistor with impurities during theformation of a normal transistor and a phototransistor. In this case, analignment process for covering a channel region by a mask has to beperformed, and this leads to a decrease in production yield in themanufacture of a thin film transistor. Therefore, a solution for thisproblem is required.

BRIEF SUMMARY

An exemplary embodiment of the disclosure in this document provides athin film transistor, comprising: a first transistor region and a secondtransistor region defined on a substrate; and a first transistor and asecond transistor respectively disposed on the first and secondtransistor regions, the first transistor comprising: a firstsemiconductor layer having source, channel, and drain regions defined onthe substrate; a first insulating film disposed on the firstsemiconductor layer; a first transparent electrode disposed on the firstinsulating film and formed corresponding to the channel region of thefirst semiconductor layer; and a second insulating film disposed on thefirst transparent electrode, and the second transistor comprising: asecond semiconductor layer having source, channel, and drain regionsdefined on the substrate; the first insulating film disposed on thesecond semiconductor layer; a second transparent electrode disposed onthe first insulating film and formed corresponding to the channel regionof the second semiconductor layer; a second gate disposed on the secondtransparent electrode; and the second insulating film disposed on thesecond gate.

In an aspect, an exemplary embodiment provides a thin film transistor,comprising: a first transistor region and a second transistor regiondefined on a substrate; and a first transistor and a second transistordisposed on the first and second transistor regions, the firsttransistor comprising: a first semiconductor layer having source,channel, and drain regions defined on the substrate; a first insulatingfilm disposed on the first semiconductor layer; a first transparentelectrode disposed on the first insulating film and formed correspondingto the channel region of the first semiconductor layer; and a secondinsulating film disposed on the first transparent electrode and havingan opening exposing the first transparent electrode, and the secondtransistor comprising: a second semiconductor layer having source,channel, and drain regions defined on the substrate; the firstinsulating film disposed on the second semiconductor layer; a secondtransparent electrode disposed on the first insulating film and formedcorresponding to the channel region of the second semiconductor layer; asecond gate disposed on the second transparent electrode; and the secondinsulating film disposed on the second gate.

In another aspect, an exemplary embodiment of the disclosure provides athin film transistor fabricating method, comprising: defining a firsttransistor region and a second transistor region on a substrate; forminga first semiconductor layer and a second semiconductor layer on thefirst and second transistor regions; forming a first insulating film onthe first semiconductor layer and the second semiconductor layer;forming a first transparent electrode corresponding to a channel regionof the first semiconductor layer and a second transparent electrodecorresponding to a channel region of the second semiconductor layer onthe first insulating film and forming a second gate on the secondtransparent electrode; and forming a second insulating film on the firsttransparent electrode and the second gate.

In another aspect, an exemplary embodiment provides a thin filmtransistor fabricating method, comprising: defining a first transistorregion and a second transistor region on a substrate; forming a firstsemiconductor layer and a second semiconductor layer on the first andsecond transistor regions; forming a first insulating film on the firstsemiconductor layer and the second semiconductor layer; forming a firsttransparent electrode corresponding to a channel region of the firstsemiconductor layer and a second transparent electrode corresponding toa channel region of the second semiconductor layer and forming a firstgate and a second gate on the first transparent electrode and the secondtransparent electrode, respectively; forming a second insulating film onthe first transparent electrode and the second gate; forming an openingexposing the first gate on the second insulating film; and removing thefirst gate exposed through the opening formed on the second insulatingfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompany drawings, which are included to provide a furtherunderstanding of the invention and are incorporated on and constitute apart of this specification illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a cross sectional view of a thin film transistor in accordancewith a first exemplary embodiment.

FIGS. 2 to 5 are process flow charts for explaining a thin filmtransistor fabricating method in accordance with the first exemplaryembodiment.

FIG. 6 is a schematic cross sectional view of an organic light emittingdisplay manufactured in accordance with the first exemplary embodiment.

FIG. 7 is a cross sectional view of a thin film transistor in accordancewith the first exemplary embodiment.

FIGS. 8 to 12 are process flow charts for explaining a thin filmtransistor fabricating method in accordance with a second exemplaryembodiment.

FIG. 13 is a schematic cross sectional view of a liquid crystal displaymanufactured in accordance with the second exemplary embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

Reference will now be made in detail embodiments of the inventionexamples of which are illustrated in the accompanying drawings.

Hereinafter, an implementation of this document will be described indetail with reference to the attached drawings.

First Exemplary Embodiment

As shown in FIG. 1, in a first exemplary embodiment, a first transistorregion T1 and a second transistor region T2 are defined on a substrate110. A first transistor and a second transistor are disposed in thefirst transistor region T1 and the second transistor region T2,respectively.

The first transistor may comprise a buffer layer 111 disposed on thesubstrate 110, a first semiconductor layer 113 having a source region113 a, a channel region 113 c, and a drain region 113 b defined on thebuffer layer 111, a first insulating film 114 disposed on the firstsemiconductor layer 113, a first transparent electrode 115 a disposed onthe first insulating film 114 and formed corresponding to the channelregion 113 c of the first semiconductor layer 113, a second insulatingfilm 117 disposed on the first transparent electrode 115 a, and a thirdinsulating film 119 disposed on the second insulating film 117.

The second transistor may comprise a buffer layer 111 disposed on thesubstrate 110, a second semiconductor layer 113 having a source region113 d, a channel region 113 f, and a drain region 113 e defined on thebuffer layer 111, a first insulating film 114 disposed on the secondsemiconductor layer 113, a second transparent electrode 115 b disposedon the first insulating film 114 and formed corresponding to the channelregion 113 f of the second semiconductor layer 113, a second gate 116 bdisposed on the second transparent electrode 115 b, a second insulatingfilm 117 disposed on the second gate 116 b, and a third insulating film119 disposed on the second insulating film 117.

In the above description, the first transistor is formed of aphototransistor having a channel formed by external light, and thesecond transistor is formed of a top gate type normal transistor havinga channel formed by a voltage supplied to the second gate.

Hereinafter, a thin film transistor fabricating method in accordancewith the first exemplary embodiment of the present invention will bedescribed.

First, as shown in FIG. 2, a first transistor region T1 and a secondtransistor region T2 are defined on a substrate 110. A buffer layer 111may be disposed on the substrate 110 on which the first transistorregion T1 and the second transistor region T2 are defined. The bufferlayer 111 may be formed to protect a transistor to be formed in asubsequent process from impurities such as an alkali ion leaking fromthe substrate 110. The buffer layer 111 may be made of silicone oxide(SiOx), silicone nitride (SiNx), or the like.

Next, as shown in FIG. 2, a first semiconductor layer 113 a, . . . , 113c and a second semiconductor layer 113 d, . . . , 113 f are formed inthe first transistor region T1 and the second transistor region T2. Thefirst semiconductor layer 113 a, . . . , 113 c and the secondsemiconductor layer 113 d, . . . , 113 f may include amorphous siliconor crystallized polycrystalline silicon.

Next, as shown in FIG. 2, a first insulating film 114 is formed on thefirst semiconductor layer 113 a, . . . , 113 c and the secondsemiconductor layer 113 d, . . . , 113 f. The first insulating film 114may be made of silicon oxide (SiOx), silicone nitride (SiNx), ormulti-layers thereof, but is not restricted thereto.

Next, as shown in FIG. 2, a transparent metal 115 is formed on the firstinsulating film 114. The transparent metal 115 may be formed of any oneof ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ITZO (Indium TinZinc Oxide), and AZO (Zno doped Al2O3), but is not restricted thereto.

Next, as shown in FIG. 2, a gate metal 116 is formed on the transparentmetal 115. The gate metal 116 may be formed of a single layer ormulti-layer formed of any one selected from the group consisting ofmolybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti),nickel (Ni), neodymium (Nd) and copper (Cu), or a combination thereof.

Next, as shown in FIG. 2, a first photoresistor PR1 and a secondphotoresistor PR2 respectively corresponding to a channel region 113 cof the first semiconductor layer and a channel region 113 f of thesecond semiconductor layer are formed on the gate metal 116.

Next, as shown in FIG. 3, portions of the gate metal 116 and thetransparent metal 115 are removed by using the first photoresistor PR1and the second photoresistor PR2, and a first gate 116 a, a firsttransparent electrode 115 a, a second gate 116 b, and a secondtransparent electrode 115 b are formed. Dry etching (D/E) may be usedfor removing a portion of the gate metal 116, and wet etching (W/E) maybe used for removing a portion of the transparent metal 115. However,the present invention is not restricted thereto.

Next, as shown in FIG. 3, source and drain regions 113 a and 113 b ofthe first semiconductor layer and source and drain regions 113 d and 113e of the second semiconductor layer are doped (Dp) with impurities. Theimpurities may be a P-type or N-type.

Next, as shown in FIG. 4, the first photoresistor PR1, secondphotoresistor PR2, and first gate 116a are removed to thus form a firsttransparent electrode 115 a corresponding to the channel region 113 d ofthe first semiconductor layer and a second transparent electrode 115 bcorresponding to the channel region 113 f of the second semiconductorlayer on the first insulating film 114 and to form a second gate 116 bon the second transparent electrode 115 b. Wet etching (W/E) may be usedfor removing the first gate 116 a, and a strip method may be used forremoving the first photoresistor PR1 and the second photoresistor PR2.However, the present invention is not restricted thereto.

Next, as shown in FIG. 5, a second insulating film 117 is formed on thefirst transparent electrode 115 a and the second gate 116 a. The secondinsulating film 117 may be made of silicon oxide (SiOx), siliconenitride (SiNx), or multi-layers thereof, but is not restricted thereto.Although not shown, a source and a drain which contact the source anddrain regions 113 a and 113 b of the first semiconductor layer and thesource and drain regions 113 d and 113 e of the second semiconductorlayer, respectively, may be disposed on the second insulating film 117.Therefore, the illustrated third insulating film 119 is formed on thesource and drain.

As for the above-described thin film transistor in accordance with theexemplary embodiment of the present invention, a mask process forcarrying out an impurity doping process on the source and drain regionsof the semiconductor layers is omitted in the process of forming aphototransistor and a normal transistor on the substrate. This isbecause, as the mask is replaced with the first and second transparentelectrodes formed on the first insulating film, a self-aligned doping isenabled. Additionally, the thin film transistor in accordance with theexemplary embodiment of the present invention can improve reliabilityand enhance production yield and product competitiveness since aphototransistor and a normal transistor have the same structure.

Hereinafter, an organic light emitting display manufactured according tothe first exemplary embodiment of the present invention will bedescribed.

As shown in FIG. 6, a first substrate 110 defining a first transistorregion T1 and a second transistor region T2 is disposed on a panel of anorganic light emitting display manufactured in accordance with the firstexemplary embodiment of the present invention.

A buffer layer 111 is disposed on the first substrate 110. The bufferlayer 111 may be formed to protect a transistor to be formed in asubsequent process from impurities such as an alkali ion leaking fromthe substrate 110. The buffer layer 111 may be made of silicone oxide(SiOx), silicone nitride (SiNx), or the like.

A first semiconductor layer 113 a, . . . , 113 c and a secondsemiconductor layer 113 d, . . . , 113 f partitioned off on the firsttransistor region T1 and on the second transistor region T2 are disposedon the buffer layer 111. The first semiconductor layer 113 a, . . . ,113 c and the second semiconductor layer 113 d, . . . , 113 f mayinclude amorphous silicon or crystallized polycrystalline silicon.

A first insulating film 114 is formed on the first semiconductor layer113 a, . . . , 113 c and the second semiconductor layer 113 d, . . . ,113 f. The first insulating film 114 may be made of silicon oxide(SiOx), silicone nitride (SiNx), or multi-layers thereof, but is notrestricted thereto.

On the first insulating film 114, a first transparent electrode 115adisposed on the channel region 113 c of the first semiconductor layerand a second transparent electrode 115 b disposed on the channel region113 f of the second semiconductor layer may be formed on the firstinsulating film 114. The first and second transparent electrodes 115 aand 115 b may be formed of any one of ITO (Indium Tin Oxide), IZO(Indium Zinc Oxide), ITZO (Indium Tin Zinc Oxide), and AZO (Zno dopedAl2O3), but are not restricted thereto.

A second gate 116 b is disposed on the second transparent electrode 115b. The second gate 116 b may be formed of a single layer or multi-layerformed of any one selected from the group consisting of molybdenum (Mo),aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni),neodymium (Nd) and copper (Cu), or a combination thereof.

A second insulating film 117 is formed on the first transparentelectrode 115 a and the second gate 116b. The second insulating film 117may be made of silicon oxide (SiOx), silicone nitride (SiNx), ormulti-layers thereof, but is not restricted thereto.

A source 118 d and a drain 118 e which contact the source and drainregions 113 d and 113 e of the second semiconductor layer are disposedon the second insulating film 117. Although not shown, the source anddrain are disposed so as to be in contact with the source and drainregions 113 a and 113 b of the first semiconductor layer.

A third insulating film 119 exposing the source 118 d or the drain 118 eis disposed on the source and drain 118 d and 118 e. The thirdinsulating film 119 may be made of silicon oxide (SiOx), siliconenitride (SiNx), or multi-layers thereof, but is not restricted thereto.

A lower electrode 120 contacting the source 118 d or drain 118 e isdisposed on the third insulating film 119. As the lower electrode 120, acathode or anode may be selected. If a cathode is selected as the lowerelectrode 120, the lower electrode 120 may be formed of any one ofaluminum (Al), an aluminum alloy (Al alloy), and aluminum neodymium(AlNd).

An organic light emitting layer 121 is disposed on the lower electrode120. The organic light emitting layer 121 may include a hole injectionlayer, a hole transport layer, a light emitting layer, an electrontransport layer, and an electron injection layer, but is not limitedthereto.

An upper electrode 122 is disposed on the organic light emitting layer121. As the upper electrode 122, an anode or cathode may be selected. Ifan anode is selected as the upper electrode 122, the upper electrode 122may be formed of any one of ITO (Indium Tin Oxide), IZO (Indium ZincOxide), ITZO (Indium Tin Zinc Oxide), and AZO (Zno doped Al2O3), but isnot restricted thereto.

In the case of the organic light emitting display having the abovestructure, a second substrate 130 may be provided and joined and sealedso as to protect an element formed on the first substrate 110 frommoisture or oxygen. The organic light emitting display manufactured asabove may comprise a data driver and a scan driver that supply a datasignal and a scan signal. Therefore, the organic light emitting displayin accordance with the exemplary embodiment can be manufactured as adisplay device capable of representing an image by a data signal and ascan signal that are supplied from the data driver and the scan driver.

Meanwhile, a phototransistor is formed in the first transistor regionT1, and a normal transistor is formed in the second transistor regionT2. In the exemplary embodiment, the first transistor formed in thefirst transistor region T1 may operates as a phototransistor for sensingexternal light, and the second transistor formed in the secondtransistor region may operate as a normal transistor for driving anorganic light emitting diode formed in a pixel area. Accordingly, theorganic light emitting display in accordance with the exemplaryembodiment is able to adjust the luminance of a pixel by means ofexternal light.

A method of adjusting the luminance of a pixel by using aphototransistor is one of the methods for adjusting the luminance of adisplay device, so that those skilled in the art may implement thepresent invention by configuring the phototransistor circuitally so asto work in conjunction with the data driver. According to the method ofadjusting the luminance of a pixel by using a phototransistor, theluminance of a pixel can be increased in a bright environment, while theluminance of a pixel can be decreased in a dark environment, therebyimproving visibility and reducing power consumption. Consequently, theexemplary embodiment can provide a thin film transistor and an organiclight emitting display that can realize an ALS (Ambient Light Sensor).

Second Exemplary Embodiment

As shown in FIG. 7, a first transistor region T1 and a second transistorregion T2 are defined on a substrate 110. A first transistor and asecond transistor are disposed in the first transistor region T1 and thesecond transistor region T2, respectively.

The first transistor may comprise a buffer layer 211 disposed on thesubstrate 210, a first semiconductor layer 213 having a source region213 a, a channel region 213 c, and a drain region 213 b defined on thebuffer layer 211, a first insulating film 214 disposed on the firstsemiconductor layer 213, a first transparent electrode 215 a disposed onthe first insulating film 214 and formed corresponding to the channelregion 213 c of the first semiconductor layer 213, and a secondinsulating film 217 disposed on the first transparent electrode 215 aand having an opening OPN exposing the first transparent electrode 215a.

The second transistor may comprise a buffer layer 211 disposed on thesubstrate 210, a second semiconductor layer 213 having a source region213 a, a channel region 213 c, and a drain region 213 b defined on thebuffer layer 211, a first insulating film 214 disposed on the secondsemiconductor layer 213, a second transparent electrode 215 b disposedon the first insulating film 214 and formed corresponding to the channelregion 213 f of the second semiconductor layer 213, a second gate 216 bdisposed on the second transparent electrode 215 b, and a secondinsulating film 217 disposed on the second gate 216 b.

In the above explanation, the first transistor is formed as aphototransistor whose channel is formed by external light, and thesecond transistor is formed as a top gate type normal transistor whosechannel is formed by a voltage supplied to the second gate.

Hereinafter, a thin film transistor fabricating method in accordancewith a second exemplary embodiment of the present invention will bedescribed.

First, as shown in FIG. 8, a first transistor region T1 and a secondtransistor region T2 are defined on a substrate 210. A buffer layer 211may be disposed on the substrate 210 on which the first transistorregion T1 and the second transistor region T2 are defined. The bufferlayer 211 may be formed to protect a transistor to be formed in asubsequent process from impurities such as an alkali ion leaking fromthe substrate 210. The buffer layer 211 may be made of silicone oxide(SiOx), silicone nitride (SiNx), or the like.

Next, as shown in FIG. 8, a first semiconductor layer 213 a, . . . , 213c and a second semiconductor layer 213 d, . . . , 213 f are formed inthe first transistor region T1 and the second transistor region T2. Thefirst semiconductor layer 213 a, . . . , 213 c and the secondsemiconductor layer 213 d, . . . , 213 f may include amorphous siliconor crystallized polycrystalline silicon.

Next, as shown in FIG. 8, a first insulating film 214 is formed on thefirst semiconductor layer 213 a, . . . , 213 c and the secondsemiconductor layer 213 d, . . . , 213 f. The first insulating film 214may be made of silicon oxide (SiOx), silicone nitride (SiNx), ormulti-layers thereof, but is not restricted thereto.

Next, as shown in FIG. 8, a transparent metal 215 is formed on the firstinsulating film 214. The transparent metal 215 may be formed of any oneof ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ITZO (Indium TinZinc Oxide), and AZO (Zno doped Al2O3), but is not restricted thereto.

Next, as shown in FIG. 8, a gate metal 216 is formed on the transparentmetal 215. The gate metal 216 may be formed of a single layer ormulti-layer formed of any one selected from the group consisting ofmolybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti),nickel (Ni), neodymium (Nd) and copper (Cu), or a combination thereof.

Next, as shown in FIG. 8, a first photoresistor PR1 and a secondphotoresistor PR2 corresponding to a channel region 213 c of the firstsemiconductor layer and a channel region 213 f of the secondsemiconductor layer, respectively, are formed on the gate metal 216.

Next, as shown in FIG. 9, portions of the gate metal 216 and thetransparent metal 215 are removed by using the first photoresistor PR1and the second photoresistor PR2, and a first gate 216 a, a firsttransparent electrode 215 a, a second gate 216 b, and a secondtransparent electrode 215 b are formed. Dry etching (D/E) may be usedfor removing a portion of the gate metal 216, and wet etching (W/E) maybe used for removing a portion of the transparent metal 215. However,the present invention is not restricted thereto.

Next, as shown in FIG. 9, source and drain regions 213 a and 213 b ofthe first semiconductor layer and source and drain regions 213 d and 213e of the second semiconductor layer are doped (Dp) with impurities. Theimpurities may be a P-type or N-type.

Next, as shown in FIG. 10, the first photoresistor Pr1 and the secondphotoresistor PR2 are removed, and a second insulating film 217 isformed on the first gate 216 a and the second gate 216 b. The secondinsulating film 217 may be made of silicon oxide (SiOx), siliconenitride (SiNx), or multi-layers thereof, but is not restricted thereto.

Next, as shown in FIG. 10, an opening exposing the first gate 216 a isformed on the second insulating film 217. Although not shown, openingsOPN are formed in the source and drain regions 213 a and 213 b of thefirst semiconductor layer and the source and drain regions 213 d and 213e of the second semiconductor layer, as well as in the region exposingthe first gate 216 a. In other words, the illustrated opening OPN isformed in the same manner simultaneously with the formation of openingsthat expose the source and drain regions 213 a and 213 b of the firstsemiconductor layer and the source and drain regions 213 d and 213 e ofthe second semiconductor layer.

Next, as shown in FIG. 11, the first gate 216 exposed through theopening OPN formed on the second insulating film 217 is removed.Although not shown, the first gate 216 a may be removed along with theremoval of portions of the source and drain which are formed on thesecond insulating film 217 so as to contact the source and drain regions213 a and 213 b of the first semiconductor layer and the source anddrain regions 213 d and 213 e of the second semiconductor layer.

Next, as shown in FIG. 12, a third insulating film 219 is formed on thesecond insulating film 217. The third insulating film 219 may be made ofsilicon oxide (SiOx), silicone nitride (SiNx), or multi-layers thereof,but is not restricted thereto.

As for the above-described thin film transistor in accordance with theexemplary embodiment of the present invention, a mask process forcarrying out an impurity doping process on the source and drain regionsof the semiconductor layer is omitted in the process of forming aphototransistor and a normal transistor on the substrate. This isbecause, as the mask is replaced with the first and second transparentelectrodes formed on the first insulating film, a self-aligned doping isenabled. Additionally, the thin film transistor in accordance with theexemplary embodiment of the present invention can improve reliabilityand enhance production yield and product competitiveness since aphototransistor and a normal transistor have the same structure.

Hereinafter, a light emitting display manufactured according to thesecond exemplary embodiment of the present invention will be described.

As shown in FIG. 13, a first substrate 210 defining a first transistorregion T1 and a second transistor region T2 is disposed on a panel of anorganic light emitting display manufactured in accordance with thesecond exemplary embodiment of the present invention.

A buffer layer 211 is disposed on the first substrate 210. The bufferlayer 211 may be formed to protect a transistor to be formed in asubsequent process from impurities such as an alkali ion leaking fromthe substrate 210. The buffer layer 211 may be made of silicone oxide(SiOx), silicone nitride (SiNx), or the like.

A first semiconductor layer 213 a, . . . , 213 c and a secondsemiconductor layer 213 d, . . . , 213 f partitioned off on the firsttransistor region T1 and on the second transistor region T2 are disposedon the buffer layer 211. The first semiconductor layer 213 a, . . . ,213 c and the second semiconductor layer 213 d, . . . , 213 f mayinclude amorphous silicon or crystallized polycrystalline silicon.

A first insulating film 214 is formed on the first semiconductor layer213 a, . . . , 213 c and the second semiconductor layer 213 d, . . . ,213 f. The first insulating film 214 may be made of silicon oxide(SiOx), silicone nitride (SiNx), or multi-layers thereof, but is notrestricted thereto.

On the first insulating film 214, a first transparent electrode 215adisposed on the channel region 213 c of the first semiconductor layerand a second transparent electrode 215 b disposed on the channel region213 f of the second semiconductor layer may be formed on the firstinsulating film 214. The first and second transparent electrodes 215 aand 215 b may be formed of any one of ITO (Indium Tin Oxide), IZO(Indium Zinc Oxide), ITZO (Indium Tin Zinc Oxide), and AZO (Zno dopedAl2O3), but are not restricted thereto.

A second gate 216 b is disposed on the second transparent electrode 215b. The second gate 216 b may be formed of a single layer or multi-layerformed of any one selected from the group consisting of molybdenum (Mo),aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni),neodymium (Nd) and copper (Cu), or a combination thereof.

A second insulating film 217 having an opening exposing the firsttransparent electrode 215 a is formed on the first transparent electrode215 a and the second gate 216 b. The second insulating film 217 may bemade of silicon oxide (SiOx), silicone nitride (SiNx), or multi-layersthereof, but is not restricted thereto.

A source 218 d and a drain 218 e which contact the source and drainregions 213 d and 213 e of the second semiconductor layer are disposedon the second insulating film 217. Although not shown, the source anddrain are disposed so as to be in contact with the source and drainregions 213 a and 213 b of the first semiconductor layer.

A third insulating film 219 exposing the source 218 d or the drain 218 eis disposed on the source and drain 218 d and 218 e. The thirdinsulating film 219 may be made of silicon oxide (SiOx), siliconenitride (SiNx), or multi-layers thereof, but is not restricted thereto.

A pixel electrode 220 contacting the source 218 d or drain 218 e and acommon electrode 221 connected to a common voltage line (not shown) aredisposed on the third insulating film 219. The pixel electrode 220 andthe common electrode 221 may be formed of any one of ITO (Indium TinOxide), IZO (Indium Zinc Oxide), ITZO (Indium Tin Zinc Oxide), and AZO(Zno doped Al2O3), but are not restricted thereto.

A black matrix 223 is disposed on the second substrate 230 facing thefirst substrate 210. The black matrix 223, which is a non-display area,is made of a photosensitive organic material having a black pigmentadded thereto. As the black pigment, carbon black or titanium oxide canbe used, but the present invention is not limited thereto.

A color filter 224 is disposed between the black matrixes 223. The colorfilter 224 may be formed of filters of red, green, and blue, or may beformed of filters of other colors. Although not shown, according to thedriving mode of the liquid crystal display, an overcoat layer may bedisposed on the black matrices 223 and the color filter 224.

In case of the liquid crystal display having the above-describedstructure, the first substrate 210 and the second substrate 230 facingeach other are joined and sealed together with a liquid crystal layerinterposed therebetween. The liquid crystal display manufactured asabove may comprise a data driver and a scan driver that supply a datasignal and a scan signal. Therefore, the light emitting display inaccordance with the exemplary embodiment can be manufactured as adisplay device capable of representing an image by polarizing lightemitted from a backlight unit by a data signal and a scan signal thatare supplied from the data driver and the scan driver.

Meanwhile, a phototransistor is formed in the first transistor regionT1, and a normal transistor is formed in the second transistor regionT2. In the exemplary embodiment, the first transistor formed in thefirst transistor region T1 may operates as a phototransistor for sensingexternal light, and the second transistor formed in the secondtransistor region may operate as a normal transistor for driving anorganic light emitting diode formed in a pixel area. Accordingly, theorganic light emitting display in accordance with the exemplaryembodiment is able to adjust the luminance of a pixel by means ofexternal light.

A method of adjusting the luminance of a pixel by using aphototransistor is one of the methods for adjusting the luminance of adisplay device, so that those skilled in the art may implement thepresent invention by configuring the phototransistor circuitally so asto work in conjunction with the data driver. According to the method ofadjusting the luminance of a pixel by using a phototransistor, theluminance of a pixel can be increased in a bright environment, while theluminance of a pixel can be decreased in a dark environment, therebyimproving visibility and reducing power consumption. Consequently, theexemplary embodiment can provide a thin film transistor and an organiclight emitting display that can realize an ALS (Ambient Light Sensor).

As described above, the exemplary embodiments of the present inventioncan provide a thin film transistor and a thin film transistorfabricating method which can improve the reliability and productionyield of a normal transistor and a phototransistor. Further, theexemplary embodiments of the present invention can provide aphototransistor capable of adjusting the luminance of a panel and adisplay device capable of improving visibility and reduce powerconsumption.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteachings can be readily applied to other types of apparatuses. Thedescription of the foregoing embodiments is intended to be illustrative,and not to limit the scope of the claims. Many alternatives,modifications, and variations will be apparent to those skilled in theart. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents but also equivalent structures.Moreover, unless the term “means” is explicitly recited in a limitationof the claims, such as limitation is not intended to be interpretedunder 35 USC 112 (6).

1. A thin film transistor, comprising: a first transistor region and asecond transistor region defined on a substrate; and a first transistorand a second transistor respectively disposed on the first and secondtransistor regions, the first transistor comprising: a firstsemiconductor layer having source, channel, and drain regions defined onthe substrate; a first insulating film disposed on the firstsemiconductor layer; a first transparent electrode disposed on the firstinsulating film and formed corresponding to the channel region of thefirst semiconductor layer; and a second insulating film disposed on thefirst transparent electrode, and the second transistor comprising: asecond semiconductor layer having source, channel, and drain regionsdefined on the substrate; the first insulating film disposed on thesecond semiconductor layer; a second transparent electrode disposed onthe first insulating film and formed corresponding to the channel regionof the second semiconductor layer; the second gate disposed on thesecond transparent electrode; and a second insulating film disposed onthe second gate.
 2. The thin film transistor of claim 1, wherein thefirst transistor comprises a phototransistor.
 3. An organic lightemitting display manufactured according to claim
 1. 4. A liquid crystaldisplay comprising the thin film transistor of claim
 1. 5. A thin filmtransistor, comprising: a first transistor region and a secondtransistor region defined on a substrate; and a first transistor and asecond transistor disposed on the first and second transistor regions,the first transistor comprising: a first semiconductor layer havingsource, channel, and drain regions defined on the substrate; a firstinsulating film disposed on the first semiconductor layer; a firsttransparent electrode disposed on the first insulating film and formedcorresponding to the channel region of the first semiconductor layer;and a second insulating film disposed on the first transparent electrodeand having an opening exposing the first transparent electrode, and thesecond transistor comprising: a second semiconductor layer havingsource, channel, and drain regions defined on the substrate; the firstinsulating film disposed on the second semiconductor layer; a secondtransparent electrode disposed on the first insulating film and formedcorresponding to the channel region of the second semiconductor layer; asecond gate disposed on the second transparent electrode; and the secondinsulating film disposed on the second gate.
 6. The thin film transistorof claim 5, wherein the first transistor comprises a phototransistor. 7.An organic light emitting display manufactured according to claim
 5. 8.A liquid crystal display comprising the thin film transistor of claim 5.9. A thin film transistor fabricating method, comprising: defining afirst transistor region and a second transistor region on a substrate;forming a first semiconductor layer and a second semiconductor layer onthe first and second transistor regions; forming a first insulating filmon the first semiconductor layer and the second semiconductor layer;forming a first transparent electrode corresponding to a channel regionof the first semiconductor layer and a second transparent electrodecorresponding to a channel region of the second semiconductor layer onthe first insulating film and forming a second gate on the secondtransparent electrode; and forming a second insulating film on the firsttransparent electrode and the second gate.
 10. The thin film transistorfabricating method of claim 9, wherein the forming of the firsttransparent electrode, the second transparent electrode, and the secondgate comprises: forming a transparent metal on the first insulatingfilm; forming a gate metal on the transparent metal; forming a firstphotoresistor and a second photoresistor respectively corresponding tothe channel regions of the first semiconductor layer and secondsemiconductor layer on the gate metal; removing portions of the gatemetal and transparent metal by using the first photoresistor and thesecond photoresistor and forming a first gate, the first transparentelectrode, the second gate, and the second transparent electrode; dopingsource and drain regions of the first semiconductor layer and secondsemiconductor layer with impurities; and removing the firstphotoresistor, the second photoresistor, and the first gate.
 11. Thethin film transistor fabricating method of claim 9, wherein the firsttransistor comprises a phototransistor.
 12. A thin film transistorfabricating method, comprising: defining a first transistor region and asecond transistor region on a substrate; forming a first semiconductorlayer and a second semiconductor layer on the first and secondtransistor regions; forming a first insulating film on the firstsemiconductor layer and the second semiconductor layer; forming a firsttransparent electrode corresponding to a channel region of the firstsemiconductor layer and a second transparent electrode corresponding toa channel region of the second semiconductor layer and forming a firstgate and a second gate on the first transparent electrode and the secondtransparent electrode, respectively; forming a second insulating film onthe first transparent electrode and the second gate; forming an openingexposing the first gate on the second insulating film; and removing thefirst gate exposed through the opening formed on the second insulatingfilm.
 13. The thin film transistor fabricating method of claim 12,wherein the forming of the first transparent electrode, the secondtransparent electrode, the first gate, and the second gate comprises:forming a transparent metal on the first insulating film; forming a gatemetal on the transparent metal; forming a first photoresistor and asecond photoresistor respectively corresponding to the channel regionsof the first semiconductor layer and second semiconductor layer on thegate metal; removing portions of the gate metal and transparent metal byusing the first photoresistor and the second photoresistor and forming afirst gate, the first transparent electrode, the second gate, and thesecond transparent electrode; doping source and drain regions of thefirst semiconductor layer and second semiconductor layer withimpurities; and removing the first photoresistor, the secondphotoresistor, and the first gate.
 14. The thin film transistorfabricating method of claim 12, wherein the first transistor comprises aphototransistor.